This invention relates generally to multi-layer injection molding apparatus and more particularly to such apparatus having melt transfer bushings extending from a rear melt distribution manifold across an insulative air space into bores extending through a front melt distribution manifold.
Injection molding apparatus for making multi-layered protective containers for food or preforms or parisons for beverage bottles are well known. Often the inner and outer layers are made of a polyethylene terephthalate (PET) type material with one or more barrier layers made of a material such as ethylene vinyl alcohol copolymer (EVOH) or nylon. In some multi-cavity apparatus the two different melts are distributed through a single melt distribution manifold having different passages. However, preferably for materials such as these having different injection temperatures of about 565.degree. F. and 400.degree. F. respectively, the two melts are distributed through two different melt distribution manifolds. In some cases, the two melts are injected sequentially, while in other cases both coinjection and sequential injection are utilized. The two materials are injected through heated nozzles, each having a central melt channel and one or more annular melt channels extending around the central melt channel to a gate leading to the cavity.
As seen in U.S. Pat. No. 5,223,275 to Gellert which issued Jun. 29, 1993, it is also known to separate the front and rear melt distribution manifolds by a insulative air space with the melt from the rear melt distribution manifold flowing through a flat spacer washer mounted between the two manifolds. While this is suitable for some applications, it has the disadvantage that there is not sufficient thermal separation between the front melt distribution manifold and the melt from the rear melt distribution manifold flowing through it.